Subterranean termites most often enter structures from the surrounding soil to feed on wood, or other cellulosic material, of the structure and its contents. If unchecked, termites can cause considerable damage. As a result, efforts to erect physical or chemical barriers to prevent the entrance of termites into a structure or to exterminate the termites after they have invaded a structure have proven a considerable expense to the public (Su, N. Y., J. H. Scheffrahn [1990] Sociobiol. 17(1):77-94). The cost to control termites in the United States exceeds one billion dollars annually (Mauldin, J. K., S. C. Jones, R. H. Beal [1987]. The International Research Group on Wood Preservation Document No. IRG/WP/1323).
Subterranean termites construct an extensive foraging gallery beneath the soil surface. A single colony may contain several million termites with foraging territory extending up to 300 feet (Su, N. Y., R. H. Scheffrahn [1988] Sociobiol 14(2):353-359). Since subterranean termites are a cryptic creature, their presence is not normally known until after some damage, foraging tubes, or live termites such as swarmers, are found. Some subterranean termites are known to forage beneath an object on the soil surface (Ettershank, G., J. A. Ettershank, W. G. Whitford [1980] Environ. Entomol. 9:645-648).
Currently, there are two basic approaches for the control of subterranean termites: preventive control and remedial control. In some of the United States, it is mandatory that the soil underlying the foundation of newly constructed buildings be pre-treated with a pesticide (also referred to herein as termiticide) to prevent termite infestation. Pesticide is typically sprayed over and into the soil prior to construction. This pre-construction treatment produces a horizontal barrier beneath the building. Because of the lack of communication between pesticide applicator and construction workers, the barrier often loses its continuity during the construction. Moreover, the currently available soil termiticides tend to lose their biological activity after five or more years to the extent that the treated soil is no longer effective against termite invasion. Established termite colonies in the soil may then invade the structure if additional chemical is not applied beneath and around the structure.
When a house or other building is infested by subterranean termites, efforts are made to create a continuous barrier beneath the building in the soil where the subterranean termites are provided access to the building. A common method of creating this barrier is to introduce termiticide around a building foundation by injection into soil underlying concrete foundations, drenching the soil surrounding the building perimeter, or a combination of both. This type of post-construction treatment is labor-intensive and may not adequately produce a continuous barrier (Frishman, A. M., B. L. Bret [1991] Pest Control 59(8):48, 52, 54, 56; Frishman, A .M., A. St. Cyr [1988] Pest Control Technology 16(4):33, 34, 36).
Other remedial treatments include spot treatments such as dusting or injecting termiticides within the walls of the building. Robert Verkerk has described arsenic trioxide dust treatment using termite lures (Verkerk, R. [1990] Building Out Termites, Pluto Press Australia Limited, P.O. Box 199, Leichhardt, NSW 2040). Verkerk describes the use of stakes or blocks of termite susceptible timber to lure termites after the stakes or blocks have been placed near a known termite problem. Once termite activity is observed, arsenic trioxide is injected. Alternatively, a portion of the termites may be dusted with arsenic trioxide.
Most spot treatments are done to stop existing termite infestations at a particular area in a structure but generally affect only a small portion of the subterranean termite population, i.e., those termites which come into direct contact with the pesticides. Because of the extensive foraging populations and expansive territory of subterranean termite colonies, the vast majority of the termite population is not affected by such spot treatments.
U.S. Pat. No. 3,940,875 describes a method, however impractical, for dispensing termite poison in the soil in an attempt to extend the life of the barrier type treatment such that the presence of termites is signalled by the release of an odor when the termites feed on the poison. The ""875 patent also describes a termite-edible container which gives off an odor when eaten by a termite. In addition to the ""875 patent and the Verkerk article referenced above, other publications describe the use of termite-edible materials as components of schemes to control termites. For example, Japanese patent application Nos. 61-198392 and 63-151033 describe wooden vessels specifically designed to xe2x80x9cattractxe2x80x9d termites as part of a monitoring procedure. The 61-198382 application describes a vessel, preferably made from pine or cedar, used in an attempt to attract termites. The 63-151033 application also uses a wood attractant to entice termites. In the 63-151033 application, the termites are further exposed to a toxicant which is then presumably carried back to the nest in hopes of killing the queen via trophallaxis or food exchange. Neither Japanese application provides any data establishing that the described process actually has any impact on termite populations. Furthermore, there is no indication that it is possible to xe2x80x9cattractxe2x80x9d termites at all. These methods have further important disadvantages. For example, the wooden inducing body will be subjected to fungal decay before termite attack, especially in moistened soil. Thus, frequent replacement of the inducing body is needed during the monitoring period. Further, damage to the inducing body can result in the penetration of the termiticide into the ground. This is not environmentally acceptable.
One termite control method comprises placing a highly toxic material such as an arsenic-containing dust, at a site of infestation in the hope that this will directly control an effective number of termites at the site and also other termites back in the colony. However, this method relies on pumping toxic dust into a termite tunnel and depositing relatively large quantities of dust.
Elaborate schemes of pipes to convey liquid termiticides under and surrounding buildings have also been proposed for termite control. It has been suggested that these liquid termiticides may be dispensed into the soil surrounding and below the building through these pipes to provide a continuous barrier to the incursion of termites. This method requires a large quantity of termiticides in order to saturate the soil surrounding the building.
U.S. Pat. No. 5,027,546 describes a system intended for use on above ground termites, i.e., drywood termites, which controls termites by freezing with liquid nitrogen. Although the liquid nitrogen is essentially non-toxic in that no toxic residues persist, it is hazardous to use and the method is a spot treatment and will not affect the majority of termites. U.S. Pat. No. 4,043,073 describes a method which attempts to circumvent the problem of repeated application of pesticide. The described method functions by xe2x80x9cencapsulatingxe2x80x9d the insecticide, thus making it more persistent. The overt use of pesticides and their persistence in the environment are not remedied by this system. Another proposed system which fails to alleviate the problem of transferring insecticide directly into the soil is U.S. Pat. No. 3,624,953. This method employs a reservoir of insecticide wherein the vapors of the insecticide are permitted to permeate the soil surrounding the reservoir. Thus, exposure of the environment with toxic substances is not avoided by using this method.
Toxicants which have less environmental effect and which show activity against termites are known (Su, N. Y., M. Tamashiro, M. Haverty [1987] J. Econ. Entomol. 80:1-4; Su, N. Y., R. H. Scheffrahn [1988] Florida Entomologist 71(1):73-78; Su, N. Y., R. H. Scheffrahn [1989] J. Econ. Entomol. 82(4):1125-1129; Su, N. Y., R. H. Scheffrahn [1990] Sociobiol. 17(2):313-328; Su, N. Y. [1991] Sociobiol. 19(1):211-220; Su, N. Y., R. H. Scheffrahn [1991] J. Econ. Entomol. 84(1):170-175; Jones, S. [1984] J. Econ. Entomol. 77:1086-1091; Paton, R., L. R. Miller [1980] xe2x80x9cControl of Mastotermes darwiniensis Froggatt (Isoptera: Mastotermitidae) with Mirex Baits,xe2x80x9d Australian Forest Research 10:249-258; McHenry, W. E., U.S. Pat. No. 4,626,528; Henrick, C. A, U.S. Pat. No. 5,151,443). However, none of these toxicants have previously been used in conjunction with a method which efficiently and efficaciously delivers the toxicant to a target pest.
Australian Patent No. 1,597,293 (the ""293 patent) and a corresponding Great Britain Patent, No. 1,561,901, describe a method which involves mixing insecticide with a food matrix comprising cellulose and a binding agent The method described in the ""293 patent relies on the termite ingesting the insecticide along with the matrix, then returning to the colony to introduce the insecticide to other termites through the natural process of trophallaxis (food exchange between termites). However, the ""293 patent describes usages only when termites are known to be present and, furthermore, the described method fails to ensure that the termites will initially find the matrix and relies on those termites finding the matrix to transfer sufficient amounts of the insecticide to the colony solely by trophallaxis. Like the Japanese patent application No. 63-151033, the method of the ""293 patent requires that the matrix is more attractive to the termites than surrounding materials. The method described in the ""293 patent relies on the moisture in the matrix (supposedly retained by the binding agent, agar) to attract termites. The described method, therefore, is primarily for termite species that are attracted to moisture (or those under xe2x80x9cwater stressxe2x80x9d). Moreover, the ""293 method fails to assure that the moisture will remain in the baits when applied in the field awaiting termite arrival. This is an unrealistic requirement for a practical application, because even a moistened sawdust-agar matrix will desiccate within a few days when placed in a dry soil.
It should be noted that attractants other than water for termites have been investigated. For example, the extract from brown-rot fungi chemically resembles the trail-following pheromones of termites. Natural pheromones, however, are species and even colony-specific. A pheromone that is xe2x80x9cattractivexe2x80x9d to one species or colony of termites may repel termites of other species or colonies. It is of uncertain value, therefore, to incorporate pheromone mimics (such as the brown-rot fungi extract) in a bait, especially if a bait is to be used against a wide range of termite species.
It should also be noted that trophallaxis is an uncertain means of delivering the insecticide to the colony because it assumes that digestive enzymes and other metabolic processes do not affect the active ingredient. However, once the insecticide is ingested by the termite, the insecticide may be rendered inactive by the digestive process of the termites. Moreover, suppression of a termite population requires that a substantial number of termites in the colony are disabled before their damage potential is diminished. Relying only on trophallaxis to transfer the toxicant does not ensure that adequate numbers of termites will be controlled.
Modifications to the method described in the ""293 patent may not increase the bait intake of termites. For example, the ""293 method requires that the matrix mixture be applied at a known infestation site such as a termite mound or tree trunk. This method, therefore, can be used only as a remedial treatment. The ""293 method cannot be used unless activity of termites is detected. The ""293 patent also proposes that a large quantity of toxicant bait be placed at random locations as a preventative measure. However, without providing a procedure for detecting termites, the majority of this bait may desiccate or degrade due to fungal growth and become unpalatable to termites. Moreover, an unnecessarily large quantity of toxicant is applied in the environment.
It is therefore highly desirable to more effectively control termites or other insects in a manner which assures that the termites or other insects of interest are exposed to the toxicant, which minimizes environmental harm by reducing the amount of insecticide used, and which affects adequate numbers of termites in a colony.
The invention disclosed and claimed herein relates to a method for controlling populations of pests. The invention is most advantageously used for controlling the population of social insects which communicate through chemical signals. Specifically exemplified herein are methods and devices for the control of insects of the order Isoptera, particularly, termites.
One preferred method of the subject invention is most easily thought of as comprising two steps. These two steps can be repeated to form a multistep process or the two steps can be conducted concurrently. One step involves monitoring and/or capturing target pests by a means which does not employ the use of any pesticide. This step functions to detect the presence of pests. In addition, this monitoring step can also function as a means to capture the pest without causing the pest substantial harm or disturbance of colony activity. In the embodiment of the invention wherein pests are captured, the captured pest is still alive and, preferably, capable of moving, eating, and producing chemical signals which can attract fellow pests. This step of the process, wherein the pests are detected or captured is hereinafter referred to as the xe2x80x9cmonitoringxe2x80x9d step.
The other step of the process involves controlling a population of pests once they have been detected. The pests may have been detected, for example, as a result of the monitoring step. In the control step of the process, the pests are controlled as a result of ingesting or otherwise contacting a toxicant. The subject invention has been discovered to be highly effective in controlling even extremely large termite colonies. Advantageously, the control method utilizes only very small amounts of toxicant, and this toxicant is applied in a strictly defined and controlled manner to minimize exposure of the environment to toxicants. The use of toxicant is confined in terms of the very limited quantity and coverage of the toxicant, and in terms of the period during which the toxicant is used. Once control is attained, the monitoring step can continue. These steps can also be conducted simultaneously.
Specific carriers of toxicants, such as bait or tracking powder, are aspects of the subject invention. These carriers are referred to herein as matrices. Also described are apparatuses for presenting the toxicant-containing matrix to the target pest.
In a preferred embodiment of the invention, the control step of the process can utilize pests which have been captured in the monitoring step. Specifically, these captured pests can be used to attract or recruit other pests to the toxicant-containing matrix, herein referred to as xe2x80x9cself-recruitment,xe2x80x9d and, in some instances, to deliver toxicant to a nest or colony of the pests. The unique use of captured pests to make the toxin matrix more attractive to nestmates is referred to herein as xe2x80x9cself-recruitment.xe2x80x9d As described herein, a captured pest can be induced to chew or move through a toxicant-containing matrix before travelling to the nest. In a preferred embodiment of the subject invention, the toxicant is relatively slow-acting so the pest can travel through the colony territory before dying. Because the termite leaves the toxicant-containing matrix before dying, this method prevents the tainting of the carrier and vicinity of the matrix with dead or dying termites. In the course of traveling within the nest, the pest can leave a chemical trail directing or recruiting other of the target pests to the toxicant-containing matrix. Also, the captured pests can leave chemical signals in the toxicant-containing matrix itself, communicating the desirability of the food. Because these chemical markers are species- and even colony-specific, these chemicals are highly advantageous for self-recruitment of nestmates to the toxicant-containing matrix. Also, the pest may deliver toxicant to the nest, for example, via trophallaxis or cannibalism, where the toxicant can kill other nestmates. The effect of this method is to make the toxicant-containing matrix much more attractive to the termites. This attractiveness can result from the highly specific trail pheromones which direct other nestmates to the toxicant-containing matrix and, more importantly, the deposit in the toxicant-containing matrix of feeding-initiating pheromones which can be highly specific for the particular termite colony which is to be eliminated.
The invention also relates to materials used in carrying out the novel methods. One critical element of the subject invention is the toxicant-containing matrix which can comprise a toxicant and a binder such as Methocel(copyright), agar, other cellulosic materials, other materials which are non-repellant to the target pest, or a combination of two or more of these components. Preferably, the toxicant is slowacting. If a cellulosic material is used, that material may consist of wood particles. The matrix can further comprise components which stabilize or regulate the matrix environment. For example, a humectant such as a hygroscopic component can be added to regulate the moisture content of the matrix.
Certain novel apparatuses are also used according to the subject invention. Specifically disclosed are apparatuses for monitoring and controlling populations of insects, particularly termites. For example, one such apparatus for monitoring the presence of termites simply comprises a food source as a monitoring device which can be strategically placed at sites surrounding a structure, or at an agricultural location. These monitoring devices are accessible to the pest management operator or property owner so that they can be periodically monitored for evidence of the presence of termites. Other apparatuses, such as electronic devices, can be incorporated in the monitoring devices to alert the homeowner or pest control operator to the presence of termites. Where ground or soil surrounds a structure to be monitored for termites, the monitoring device can be placed in the soil near the structure or area to be monitored. Where no soil is around a structure or when foraging galleries are detected above ground, the monitoring device or toxicant-containing matrix can be placed above ground. Advantageously, the monitoring device can be constructed so that pests can be removed easily and without substantial harm resulting to the pest, thereby allowing the pest to be used to recruit other nestmates to the matrix.
Another apparatus useful according to the subject invention comprises a housing which is specifically designed to enclose either a monitoring device or toxicant-containing matrix. This housing is useful for protecting the monitoring device and/or toxicant-containing matrix from the environment. The monitoring device or matrix can be enclosed within the housing in such a manner so they can be removed with minimal disruption to the foraging termites. This housing is preferably made from a durable, non-biodegradable material.
The present invention provides an environmentally safe termite control system requiring no complex machinery. The invention provides apparatuses and methods for the monitoring of, and delivery of a toxicant to, a target pest wherein the apparatuses may be easily and safely serviced by property owners as well as professional pest management workers.
Advantageously, the disclosed materials and procedures minimize the risk of exposure to persons handling toxicants and increase toxicant intake by termites. The methods of the subject invention can drastically reduce pesticide use in the urban environment. Moreover, this invention can be an important part of an Integrated Pest Management (IPM) approach. The first phase of the IPM can be designed to monitor termite activity. No pesticide need be used until termite activity is detected. When activity is detected, the second phase of the IPM can be employed wherein only a small quantity of pesticide is used to control the entire colony population. Once control is achieved, the monitoring step can be repeated, as can the control step, if necessary, thus providing indefinite protection to the structure or agricultural site.
As described more fully herein, there are a variety of methods and apparatuses which can be utilized to practice the method of the subject invention. The precise methods and apparatuses which would be optimal for a particular target pest and environmental setting would be apparent to a person skilled in this art using the teachings provided herein.
The descriptions and teachings which follow primarily focus on the control of termites. Specific methods and apparatuses for the control of termites are provided, but variations of these methods and apparatuses and their applicability to pests other than termites would be readily recognized and used by a person skilled in this art.